Hundreds of officers, including armed-response teams, have been drafted in from neighbouring forces to help overstretched police in Greater Manchester tackle the vicious gang feud that is said to have claimed the lives of two officers, the Guardian can reveal.

Round-the-clock police patrols continued in east Manchester and Tameside as the investigation into the killings of two police officers, PCs Nicola Hughes, 23, and Fiona Bone, 32, went on against a backdrop of heightened tensions. There was tight security at Manchester city magistrates court on Friday morning as Dale Cregan, 29, appeared before magistrates charged with four murders – those of the two constables and Mark Short, 23, and his father David, 46. He was remanded in custody and will appear before the city's crown court on Monday.

Criminals have been active in the city as the attention of the force concentrates on the violent fallout ascribed to a long-running feud between two crime families around the Droylsden and Clayton districts to the east.

On Wednesday night, masked raiders dressed in high-visibility jackets walked into Selfridges in Manchester city centre, smashing display cabinets with axes and crowbars and grabbing £500,000 of watches in an audacious 80-second raid.

It was an attack that sources say was not a coincidence, as police focused on Tameside and Old Trafford where Manchester United were playing that night. The feuding between the two families in east Manchester appears to have been caused by an incident when a woman was slapped in the face by a man in a pub in east Manchester earlier this year. The incident lit the touchpaper for violence, the like of which has not been witnessed in Greater Manchester, involving grenades and firearms.

Senior officers believe that organised crime "does not get noticed and is dismissed by many as something that involves criminals against criminals". A police source said that the feud between the two families has been going on for 10 years.

In recent times, scant intelligence has been passed on to police and all appeared quiet, until the pub incident. While people were happy to give information to the police, few were willing to make formal statements, perhaps for fear of repercussions. Both families involved in the feud allegedly run chaotic criminal empires. They are suspected of focusing on cannabis farms, illegal property deals and the handling of stolen goods, "fencing" on a vast scale. Extortion and violence go hand in hand with their activities.

This week, Garry Shewan, the assistant chief constable, urged the two crime families to end the feud and said that Tuesday was a watershed and "enough is enough". Greater Manchester police's chief constable, Sir Peter Fahy, has said that those who believe organised crime has nothing to do with them, need to think again: "The important thing is for people to realise this is not the stuff of films or books. When you have jewellery stolen or a car stolen, when you are burgled, when there is drug dealing in your area, it is these kinds of criminal outfits that are doing it. Some people think it doesn't effect them; it does."

Gun crime has fallen dramatically in Manchester, which in the 1980s and 90s struggled to shake off the nickname of Gunchester. But serious firearms are still available, with one source claiming in the Manchester Evening News this week that hand grenades can be purchased for as little as £50 if you know where to look.

An American man, Steven Greenoe, smuggled more than 60 high-powered weapons into Britain in 2010 through Manchester airport in his luggage. He is now in jail in the United States but the vast majority of the firearms he trafficked are still in circulation and have been used before in shootings in Manchester and Merseyside.

The firearms include 11 Glock 19 handguns, which have a magazine containing 15 rounds. Latest statistics show that in Greater Manchester between April 2011 and March 2012 there were 39 firearms fired, resulting in deaths of four occasions. Gun crime has been falling, year on year, for the last decade. In contrast, at the height of the "Gunchester" era, 27 people died and 250 were injured over a troubled five-year period.

The history of Manchester gangs is by no means a new problem – it dates back to the late 19th century, when parts of the city were the turf of the most feared "scuttlers", with rival gangs engaging in fatal knife battles. In recent years, the focus has predominantly been south of the city centre, in Longsight and Moss Side, where high unemployment and the arrival of crack cocaine prompted a violent war on the streets.

Operation Xcalibre was set up eight years ago to tackle the guns menace that was blighting communities and affecting the national perception of the city. The breakthrough came three years later following the shooting of Tyrone Gilbert at the funeral of Ucal Chin, a young father with friends in the Longsight crew. The rival Gooch gang leaders Lee Amos and Colin Joyce opened fire into a crowd of mourners as they drove into the crowd of 90 people. Senior police described the pair as psychopaths.

When 11 members of the gang were later convicted at Liverpool crown court following an intensive police operation, shootings tailed off enormously. But there are new, worrying trends emerging.

The violence has switched to areas such as Salford – where innocent Indian postgraduate student Anuj Bidve was murdered on Boxing Day last year by Kiaran Stapleton after he inadvertently wandered into his patch – and to the deprived estates east of the city. Hattersley has struggled to shake off its reputation following the Moors murders in the 1960s, since Myra Hindley and Ian Brady lived nearby. And Britain's most prolific serial killer, Dr Harold Shipman, who murdered 215 patients, lived and worked just up the road in Hyde.

On the Hattersley estate in Mottram where the officers died, residents began to speak out against the perception that the community routinely presented a wall of silence to the police. Lisa Holmes said the vast majority of locals were not criminals and dismissed the suggestion that known members of crime groups were treated as folk heroes.

"The suggestion that children on the estate welcome home violent criminals and look up to them is wrong," she said. "My child attends Arundale primary school on John Kennedy Road and as a mother, I know most of the children there. They are frightened at the thought of the criminals and certainly wouldn't sit praising them and welcome them to their area where they play."

Along with other residents, she's organising a vigil for the officers next week and added: "Hattersley doesn't stand for what happened on that fateful day."

Patsy Mckie, founder of the charity Mothers Against Violence, established to combat gang violence in south Manchester, said: "What we are seeing now is feuding families, rather than just gangs. I've seen a change in what's happening with regards to gangs."

When she began her work, she said the gangs were involved in violence within their own community in Moss Side and Longsight. "They were shooting each other for different kinds of reasons. It might have started off with drugs, it might be to do with guns. Or where you live, or don't live, where you can move or not move, the young people decided the lines drawn in sand. But what we are seeing now is feuds."

She acknowledges that there have always been feuds, but now she believes the emphasis is shifting, "which makes us think about the responsibilities of communities and how they live their lives and [take] responsibility for things that happen there," she added.

Three miles east of the city centre, past Manchester City's stadium, Clayton, where David Short died on 10 August, is poor, but fiercely proud, a tight-knit community of red-brick council homes.

Canon Ansbro, of St Willibrords Roman Catholic church, officiated at Mark Short's funeral. "They weren't regulars at church," he said. "They came here because they wanted us to hold Mark's funeral. I'd not seen him myself for years, since he was at school. But I met his father and mother. I don't really know them, but I took the funeral as the family requested it."

A publican in Clayton, perhaps reflecting the reluctance to speak about Short, told the Guardian: "I did know David Short and I do know of him but I'd rather not say any more."

The Rev Rob Weir, who is a methodist minister in Clayton, said people were wary of walking through the nearby nature reserve at night, but generally the area is not as bad as it is often portrayed in the media.

"I know someone in the area who had to go through a police cordon to get to their house after the murder of David Short, but not the main players. In Clayton, there are an awful lot of people who are just going about their everyday lives, and something like this where people are throwing grenades near where they live is shocking as it happened on their doorstep."

Tony Lloyd, Manchester central MP and Labour candidate for the city's first elected police commissioner, said that a lot of people who live in Clayton lead normal lives and that the activities of the criminal families do not impinge on them.

He pointed out that gun crime in the city is at a 10-year low. He is not in favour of arming the police and said that the majority of those in Mottram had greeted the police officers' deaths with "shock, horror and disbelief and a sense of impotence".